Conventionally, a technique for capturing an image of periphery of a vehicle by one or more cameras to recognize a physical object present around the vehicle has been proposed. The patent document 1 below discloses a technique for recognizing a physical object such as a bicycle present in front of a subject vehicle and identifying a direction of a sight line of a driver of the bicycle. When the sight line of the driver is not directed to the vehicle, a warning is issued.    Patent Document 1: Japanese Patent Publication Laid-Open (JPA) No. 2005-165422